Apparatus for producing carbon black

ABSTRACT

An injection assembly for introducing a plurality of laterally spaced sprays of a normally liquid hydrocarbon feedstock into the cracking zone of a carbon black furnace.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a carbon black producing feedstock injectionapparatus for use in the oil furnace process for the production of treadgrade rubber reinforcing carbon black.

2. Description of the Prior Art

The oil furnace process for obtaining high abrasion resistant carbonblacks for rubber reinforcing applications, particularly automotivetires, known in the relevant industry as the HAF, ISAF and SAF types,basically consists of contacting atomized droplets of a normally liquidhydrocarbon feedstock with an extremely turbulent mass of combustionproducts resulting from burning a mixture of fuel gas and excesspre-heated air. In accordance with the foregoing method, a major portionof the feedstock is pyrolytically dissociated in a partial oxidationreaction to provide a substantial yield of carbon black in the form ofan aerosol from whence pulverulent carbon black is recovered and thenpelleted. Beyond the particle size requirement of the respective gradesof carbon black mentioned, there are other important quality standardsthat must be met, foremost of which is structure. Structure isessentially the inherent tendency of the nascent carbon black particlesto agglomerate to form chain-like units or clusters of the particlesduring and immediately subsequent to the completion of the pyrolysisreaction. The structure characteristic is very important insofar as itrelates directly to certain critical properties exhibited by curedcarbon black reinforced rubber compositions. It will suffice to say,however, that the carbon black manufacturing art as presently practicedis highly sophisticated and thus those skilled in this art are wellaware of the combination of processing parameters needed to provide aquality product.

Lately, however, an additional quality standard for tread grade rubberreinforcing carbon black has been assuming importance. Such concerns theparticle size distribution of the resultant product. Essentially theimprovement being sought in this regard is to produce a product composedof more uniform particle sizes and particularly, the elimination of thelarger particle size component associated with the heretofore standardproducts. In this connection, particle size refers to the size of theresultant agglomerates. These new products are referred to as high tintblacks, named so because of the empirical test method utilized tomeasure this property.

It is known in the art that the manner whereby the feedstock is injectedinto the furnace, specifically at or near the center of the situs ofmaximum turbulency of the cracking gases, leads to the formation of hightint black. However, this expedient results in a product havingunacceptably low structure properties. In order to increase structure,the feedstock injector can be moved upstream of the high turbulence zoneto provide for a broader feedstock spray pattern as it enters the highturbulence zone. This unfortunately attenuates tint by increasing theagglomerate size distribution, so to compensate the reaction time mustbe shortened. This practice, however, reduces yield and calls for anexpensive drying operation to rid the final product of unreacted oil sothat the carbon black will meet the stain test imposed by the consumingrubber industry. It is accordingly, the object of this invention toprovide a feedstock injector whose use in the oil furnace processfacilitates the production of high tint carbon black withoutexperiencing the shortcomings mentioned above.

SUMMARY OF THE INVENTION

In accordance with the present invention an injection assembly isprovided which is adapted to permit the introduction of a normallyliquid hydrocarbon feedstock into a carbon black furnace as a variablyspaced array of individual sprays thereof. The contemplated assembly,from the standpoint of design, basically comprises a pipe housing orshroud containing a plurality of axially aligned feedstock supply tubesconnected to a common source of the feedstock. The individual feedstocksupply lines are adjustable as a unit with respect to said shroud topermit projections thereof from the shroud which in operation remains asa stationary part of the assembly affixed to the upstream closure end ofthe furnace. In the main, the supply tube projections are thereuponadjustable to extend same radially. The injection assembly design issuch that in operation both of the aforementioned adjustments permittingthe longitudinal and radial displacement of the feedstock supply tubesare accomplished from without the furnace.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall isometric view of the feedstock injection assembly;

FIG. 2A is a sectional view, partly in elevation, along plane 2A--2A ofFIG. 1;

FIG. 2B is a sectional view, partly in elevation, along plane 2B--2B ofFIG. 1;

FIG. 3 is a diagrammatic end-on view of feedstock supply tube spreaderplate 10 of FIG. 2B; and

FIG. 4 is a diagrammatic illustration of the placement of the feedstockinjection assembly of FIG. 1 in a carbon black furnace utilizing a chokesection for developing turbulent effluent flow conditions therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purpose of describing how the feedstock injector of thisinvention is intended to be used in practice, it would be firstlydesirable to discuss generally but briefly the furnace design commonlyutilized in the production of the abrasion resistant types of rubberreinforcing carbon blacks. While operational variants such as feedstockrate, air pre-heat temperature and rate, duration of the reaction, aswell as the composition of the feedstock are important in implementingthe production of abrasion resistant blacks, the design of the furnacenevertheless remains as the most important factor. Essentially all ofthe commercial furnaces of the type under consideration are composed oftwo main structural parts; the first or upstream portion being thecombustion chamber wherein a mixture of a fuel, preferably natural gas,and an excess of combustion supporting gas, generally air, is combusted.The combustion chamber is invariably of tubular design having a diametersubstantially larger than the length thereof. The other structuralcomponent of the furnace consists of the reaction zone wherein thecarbon producing feedstock is for the most part dissociated into carbonblack. This part of the furnace is in direct communication and centrallyaligned with the downstream end of the combustion chamber. The reactionzone is likewise tubular but having a diameter substantially smallerthan the length thereof. The reaction zone is provided with quench portsat various distances longitudinally removed from the upstream openingthereof whereby quench water can be introduced to terminate the crackingreaction after the desired duration.

The modes of effluent flow are applicable in the operation of theaforedescribed furnace design. In one mode of operation the combustionair and fuel are introduced tangentially into the combustion chamber.The combusted gas accordingly enters into the reaction zone in aninwardly spiralling pattern and in so doing leads to the formation ofextremely turbulent conditions therein especially near the upstreamopening.

The other effluent flow pattern observed is that of axial flow wherebythe combustion air and fuel are burned in the combustion chamber andintroduced into the reaction zone in a generally linear manner. Thistype of flow does not create the highly turbulent conditions within thereaction zone as does the tangential flow method and therefore theupstream extremity of the reaction zone is provided with a choke or aventuri configuration in order to realize the degree of turbulencyrequired.

The linear flow method of operation is preferred in the utilization ofthis invention. A particularly suitable design for operating in theforegoing manner is the type of furnace generally illustrated in FIG. 4.Complete details with respect to this design of a furnace and theoperation thereof can be found in U.S. Pat. No. 3,060,003.

With reference to FIG. 4 preheated combustion air is introduced into theplenum 20 and flows axially within conduit 21 to combine with the fuelgas from jets 22. The flame and the resultant combustion products aredirected radially outwardly by the deflector element 23. The hotcombustion gases thereupon flow generally axially within the combustionchamber 24 near the peripheral extent thereof and then proceed radiallydownwardly along the downstream end of the combustion chamber and intothe choke 25. Accordingly, the velocity as well as turbulency of thecombustion gases are maximized in the choke section. The reactoreffluent then flows into the enlarged reaction zone or tunnel and isquenched downstream by introducing sprays of water into the tunnel.

As further shown in FIG. 4, the individual feedstock supply tubedischarge ends of the injection assembly of FIG. 1 are positionedcontiguous to and in axial alignment with the upstream opening of thechoke. Desirably, the injection assembly is designed so that thedischarge ends of the radially extendible feedstock supply tubes will,when the latter are fully extended, lie within and adjacent to theperiphery of the choke opening. In this position the tint and structureof the resultant carbon black will be maximized. In the event lessstructure is desired the radially extended portion of the supply tubescan be adjusted inwardly to the degree which provides the level ofstructure desired, without reducing tint.

As it is apparent from the foregoing discussion, the feedstock injectoris positioned within the furnace where it is subjected to intense heatexposure, generally in the order of 2800° F. or more. Accordingly, it isessential that the unit be compact in order to minimize the area exposedto the high heat environment and to permit it to be removed from thefurnace for periodic servicing through gate valve 26 without thenecessity of shutting down the furnace. Compactness in itself, however,will not serve to protect the injector for any extended period let alonemaintain the feedstock below cracking temperature and therefore the unitmust be provided with cooling means as a practical expedient, all aswill be set forth in connection with the detailed description of theinvention given below.

For a detailed description of the injector assembly of FIG. 1 referencewill now be had to FIGS. 2A and 2B. Feedstock supply pipe 1 connects tofeedstock distribution chamber or manifold 2 fabricated from pipefitting piece 3 and header piece 4. Feedstock supply pipe 1 canacceptably be 1/2 inch SCH 80 black pipe. Six segments of metal flextubes 5 of 1/4 inch ID equally spaced on a 3/4 inch diameter circle arebrazed into the header 4. Likewise, a 1/4 inch ID metal feedstock supplytube 6 positioned centrally with respect to flex tubes 5 is brazed intothe center of header 4. Feedstock supply extension tubes 7 are brazedinto the ends of flex tubes 5 and extend to about the length of saidcentrally positioned feedstock supply tube 6.

The integral combination of feedstock supply pipe 1, manifold andfeedstock supply tubes 6 and 7 are positioned within pipe shroud 8 viafeedstock supply pipe locking mechanism 18 by means of packing gland 9.Pipe shroud 8 can be acceptably a 1 inch SCH 40 pipe which is providedwith closure member or spreader plate 10 drilled to accommodate freelythe longitudinal positioning of said feedstock supply tubes. Pipe shroud8 is of sufficient length so as to allow the ends of feedstock supplytubes 6 and 5 to be pulled back substantially flush with the outsideface of tube spreader plate 10. Shroud 8 is appropriately provided withan interior shoulder as shown in FIG. 2B with which pipe fitting piece 3abuts to prevent retraction of the feedstock supply tubes throughspreader plate 10 into the shroud.

As previously mentioned, it is necessary to provide means for coolingthe portion of the injection assembly disposed within the furnace. Withreference to FIGS. 2A and 2B, such is accomplished in the depictedinjector by providing the downstream part thereof with a water-cooledjacket generally shown at 11. The water jacket can be permanentlyaffixed to the shroud member or constitute a removable part as shown,connected to the assembly by means of packing gland 12. The water-cooledjacket is preferably fabricated from heat resistant stainless steel andis appropriately connected at the upstream end thereof to a coolingwater manifold shown generally at 13. Cooling water manifold 13 iscomposed of two sections. Inlet section 14 is adapted for introducingthe cooling water and outlet section 15 is adapted for discharging same.The inlet section 14 of the manifold communicates directly with theinterior of the cooling jacket by means of quadrantly spaced tubes 16which extend longitudinally to near the downstream extremity of thejacket thereby permitting the cooling water to discharge into the jacketat this location and to return and exit through outlet section 15 of themanifold. Insofar as there is a tendency for blow back to occur withinthe downstream interior of the shroud member, it is desirable to provideadditional cooling means in order to prevent the tube spreader plate 10and the adjacent portions of the feedstock supply tubes fromoverheating. This can be readily accomplished by introducing compressedair in the inlet section 17 of the locking mechanism 18, such coolingair exiting through the spreader plate 10.

The operation of the present injector will next be described and in sodoing reference will be had to FIG. 3 in particular. The novel featureof the present invention is that by simply rotating the feedstock supplypipe 1 relative to the stationary tube spreader plate 10, the lattershown in detail in FIG. 3, the action of the segment of flex tubecoupled with manner in which spreader plate exit holes are designedcauses each tube extension 7 projecting beyond the spreader plate totake an outwardly angular position relative to the centrally disposedfeedstock supply tube 6. The net result is an equally spaced circularpattern of the discharge ends of said feedstock supply tubes 7. Thediameter of the circular pattern depends upon the length of theprojection of the indicated feedstock supply tubes beyond the spreaderplate and the relative degree of rotation of feedstock supply pipe 1.

The tube spreader plate 10 serves to permit supply tube extensions 7 toassume a given angular position upon rotation of the feedstock supplypipe 1. As illustrated in FIG. 3, this is accomplished by the manner inwhich the holes 19 of the spreader plate 10 are provided. Firstly, holeshaving a diameter slightly larger than that of the tubing to beaccommodated are drilled perpendicular to the face of the spreaderplate. Next superimposed drillings are effected at an acute angle withrespect to the face of the spreader plate and along an axis inclinedtoward the periphery of said plate.

What is claimed is:
 1. An injection assembly for introducing a normallyliquid hydrocarbon feedstock into a carbon black producing furnace,which comprises:a pipe shroud member having an upstream and downstreamclosure end; a feedstock supply pipe concentrically disposed within saidshroud member adapted to be rotatably and longitudinally positionedtherein and whose upstream end projects beyond the upstream closure endof the shroud member; a cylindrical manifold rigidly attached to and inopen communication with the downstream end of said feedstock supply pipeand the header end of which is provided with a centrally locatedcircular port and a plurality of like ports circumferentially disposedthereabout; a metallic feedstock supply tube rigidly connected to and inaxial alignment with said centrally located circular port and projectingbeyond the shroud member downstream closure end; a metallic feedstocksupply tube rigidly connected to and in axial alignment with each ofsaid circumferentially disposed ports via a segment of metallic flextube the combined length thereof being about that of said centrallydisposed feedstock supply tube; and a spreader plate forming thedownstream rigidly affixed closure end of the shroud member and which isperforated and positioned to accommodate freely the longitudinal passageof said feedstock tubes.
 2. An injection assembly in accordance withclaim 1 wherein the linear portion thereof disposed within a furnace isprovided with a watercooled jacket.
 3. An injection assembly inaccordance with claim 2 having means for introducing cooling air intosaid shroud member near the upstream extremity thereof.
 4. An injectionassembly in accordance with claim 3 having six circumferentiallydisposed feedstock supply tubes about said concentrically disposedfeedstock supply tube.
 5. An injection assembly in accordance with claim4 wherein said water-cooled jacket is an integral part thereof.